This invention relates to a microsphere adhesive and in particular to a microsphere adhesive that exhibits enhanced adhesion to substrates while remaining repositionable.
Repositionable adhesives are commonly used for temporary messaging or signage in the home and office environment. This type of product is typified by Post-it(copyright) brand notes. When using such a product it is desired that the note adhere to a variety of surfaces yet be cleanly removable from the surface without leaving adhesive residue, while maintaining the repositionable characteristics of the notes.
References can be cited for the preparation and/or use of inherently tacky, polymeric microsphere adhesives (see for example, U.S. Pat. Nos. 3,691,140 and 4,166,152). Such microsphere adhesives are typically used for the commonly recognized repositionable notes.
Various investigators have sought to improve or further enhance adhesion to surfaces other than the commonly used paper surfaces. Various techniques have been used, such as chemical modification of the microsphere, alteration of the adhesive composition, including the use of binders and the like, or process modifications. For example, U.S. Pat. No. 5,053,436 describes a hollow microsphere, wherein the microsphere provides increased resistance to adhesive transfer and an increased adhesion level. Along the same line, U.S. Pat. No. 4,988,567 describes microspheres having multiple small voids.
In yet another attempt, U.S. Pat. No. 5,326,842 describes a dual polymerization process wherein high tack adhesives are produced wherein a chain transfer agent is used in the first step (suspension polymerization) and the second step (emulsion polymerization) provides stability of the final material.
However, to date, control of the solvent soluble portion of the microsphere to produce a stable repositionable microsphere adhesive with enhanced adhesion has not been contemplated.
Briefly, in one aspect of the present invention, a microsphere adhesive composition is provided comprising a 30-98% solvent soluble portion.
In particular, the present invention comprises a microsphere adhesive composition comprising:
(a) a plurality of polymeric, elastomeric microspheres wherein the microspheres are the reaction product of reactants comprising polymerizable starting materials comprising at least one C4-C14 alkyl (meth)acrylate monomer and optionally at least one comonomer,
(b) optionally, a polymeric stabilizer in an amount of between about 0.1 and about 3 parts by weight per 100 parts by weight of the microspheres, preferably about 0.1 to about 1.5 parts by weight per 100 parts by weight of the microspheres;
(c) a surfactant in an amount of no greater than about 5 parts by weight per 100 parts by weight of the microspheres, preferably no greater than 3 parts by weight and most preferably in the range of 0.5 to about 1.5 parts by weight per 100 parts by weight of the microspheres;
(d) a modifier, wherein the modifier can be at least one of a chain transfer agent, a tackifier, a solvent or the like in an amount that is sufficient to provide microspheres with a solvent soluble portion in the range of 30-98%, preferably in the range of 40-95%; and
(e) an initiator present in amounts ranging from 0.1 to approximately 2 parts by weight per 100 parts by weight of the polymerizable monomer starting material.
As used in this application, the notation xe2x80x9c(meth)acrylatexe2x80x9d refers to acrylate and methacrylate.
A modifier may be used to regulate the solvent soluble portion of the microspheres and it is added to the polymerization mixture in an amount sufficient to provide a solvent soluble portion that is in the range of 30-98%, preferably in the range of 40-95%. Various modifiers may be used within the scope of this invention and the amounts used are those that sufficiently provide the microspheres with a solvent soluble portion. Such amounts would range, for example for solvents from 1-30%, for tackifiers from 1-30% and for chain transfer agents, up to about 0.15%.
Particularly useful modifiers are chain transfer agents. To control the molecular weight of the polymer being formed in the microsphere a chain transfer agent or modifier is used. Many halogen-and sulfur-containing organic compounds function well as chain transfer agents in free radical polymerizations. Non-limiting examples of such agents are: carbon tetrabromide, carbon tetrachloride, dodecanethiol, iso-octylthioglycolate, butyl mercaptan, and tertiarydodecyl mercaptan. Particularly useful chain transfer agents are long chain mercaptans, such as dodecanethiol. The amount of chain transfer agent suitable for microsphere polymerizations is calculated on a weight basis to the entire polymerizable content. The chain transfer agent is preferably added at up to about 0.15%, more preferably up to about 0.12% and most preferably up to about 0.08%. These levels are adequate to provide a solvent soluble polymer component in the microsphere of up to about 98%.
Other useful modifiers are solvents. Examples of which are but not limited to: aliphatic or aromatic solvents such as heptane, benzene, toluene and the like; alcohols such as methanol, isopropyl alcohol, and the like; and ketones such as acetone, methyl ethyl ketone and the like. The amount of solvent suitable for microsphere polymerizations is calculated on a weight basis to the entire polymerizable content. The solvent is preferably added at up to about 30%, more preferably up to about 15% and most preferably up to about 5%. These levels are adequate to provide a solvent soluble polymer component in the microspheres of up to about 98%.
Still other useful modifiers include tackifiers and/or plasticizers. Examples of which are but not limited to: hydrogenated rosin esters commercially available from such companies as Hercules, Inc. under the tradenames of Foral(trademark), Regalrez(copyright) and Pentalyn(trademark). Tackifying resins also include those based on t-butyl styrene. Useful plasticizers include but are not limited to dioctylphthalate, 2 ethylhexyl phosphate, tricresyl phosphate, mineral oil and the like. The tackifier and/or plasticizer are preferably added at up to about 30%, more preferably up to about 15% and most preferably up to about 5%. These levels provide a solvent soluble polymer component in the microsphere of up to about 98%.
In another aspect of the present invention a one step suspension polymerization process is provided for preparing polymeric elastomeric microspheres comprising the steps of:
(a) stirring or agitating a mixture comprising polymerizable monomer starting materials comprising:
(i) at least one C4-C14 alkyl (meth)acrylate monomer and, optionally at least one comonomer;
(ii) an initiator for the polymerizable monomer starting materials present in amounts ranging from 0.1 to approximately 2 parts per weight per 100 parts by weight of the polymerizable monomer starting materials;
(iii) optionally, a polymeric stabilizer in an amount in the range of 0.1 to about 3 parts by weight per 100 parts by weight of the polymerizable monomer starting materials;
(iv) a surfactant in an amount no greater than about 5 parts by weight per 100 parts by weight of polymerizable monomer, preferably no greater than about 3 parts by weight and most preferably in the range of 0.5 to 1.5 parts by weight;
(v) water to form an oil in water suspension; and
(vi) a modifier in an amount sufficient to provide a solvent soluble portion in the range of 30-98%; and
(b) polymerizing the (meth)acrylate monomer(s) and the comonomer(s), if present; wherein microspheres are provided.
In yet another aspect, the present invention provides a two-step suspension polymerization process for preparing polymeric elastomeric microspheres from polymerizable monomer stating materials, wherein the process comprising the steps of:
(a) stirring or agitating a mixture comprising:
(i) at least one C4-C14 alkyl (meth)acrylate monomer;
(ii) an initiator for the monomer present in amounts ranging from 0.1 to approximately 2 parts per weight per 100 parts by weight of the polymerizable monomer starting materials;
(iii) optionally, a polymeric stabilizer in an amount in the range of 0.1 to about 3 parts by weight per 100 parts by weight of the polymerizable monomer starting materials;
(iv) a surfactant in an amount of no greater than about 5 parts by weight per 100 parts by weight of the polymerizable monomer starting materials, preferably no greater than 3 parts by weight and most preferably in the range of 0.5 to 2 parts by weight;
(v) a modifier in an amount sufficient to provide a solvent soluble portion in the range of 30-98%; and
(vi) water to form an oil in water suspension;
(b) at least partially polymerizing the polymerizable monomer starting materials;
(c) adding to the suspension at least one comonomer; and
(d) continuing the polymerization of the polymerizable monomer starting materials; wherein microspheres are provided.
The present invention also provides in another aspect a sheet material comprising a backing and coating of repositionable pressure sensitive adhesive described above is coated on at least one portion of at least one major surface.
Advantageously, the present invention provides a microsphere-based pressure sensitive adhesive having a high solvent soluble fraction that adheres to rough surfaces such as fabric, removes cleanly, and exhibits the ability to be reapplied multiple times if desired. Even with this enhanced adhesion to rough surfaces the microsphere adhesive will still adhere non-destructively to fragile surfaces such as paper. Furthermore, the microsphere adhesive of this invention is prepared according to resource efficient methods.
Several features of the adhesive of the present invention provide a number of desirable advantages that have heretofore been unavailable. For example several advantages include, (a) improved adhesion to various surfaces (textured surfaces, fabric, wood, painted surfaces, glass, vinyl, etc), (b) high adhesion without fiber pick or substrate damage on removal from substrates, (c) adhesive strength that remains constant or slightly builds after a period of time, and (d) a microsphere adhesive that adheres to a substrate or backing and easily removes from applied surfaces without transferring or leaving an adhesive residue on the applied surface.
The microspheres obtained in the present invention are the reaction product of (a) at least one alkyl (meth)acrylate ester wherein the alkyl group contains four to about 14 carbon atoms, preferably four to about 10 carbon atoms and, optionally, a comonomer. The comonomer, if present may be nonpolar, ionic polar or mixtures of such monomers.
Useful alkyl (meth)acrylate monomers are those monofunctional unsaturated (meth)acrylate esters, the alkyl groups of which have from 4 to 14 carbon atoms. Such (meth)acrylates are oleophilic, water dispersible, and are essentially water insoluble. Furthermore, useful (meth)acrylates are those that as homopolymers, generally have a glass transition temperature below about xe2x88x9220xc2x0 C., or if a combination of monomers is used, such a combination would produce a copolymer or terpolymer generally having a glass transition temperature below about xe2x88x9220xc2x0 C. Nonlimiting examples of such (meth)acrylates included but are not limited to, isooctyl acrylate, 4-methyl-2-pentyl acrylate, 2-methylbutyl acrylate, isoamyl acrylate, sec-butyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, isodecyl methacrylate, t-butyl acrylate, t-butyl methacrylate, isobornyl acrylate, methylmethacrylate, isononyl acrylate, isodecyl acrylate and the like, and the combination thereof.
Preferred alkyl (meth)acrylate monomers include isooctyl acrylate, isononyl acrylate, isoamyl acrylate, isodecyl acrylate, 2-ethylhexyl acrylate, n-butyl acrylate, sec-butyl acrylate and mixtures thereof.
Vinyl ester monomers suitable for use in the present invention include but are not limited to: vinyl 2-ethylhexanoate, vinyl caprate, vinyl laurate, vinyl pelargonate, vinyl hexanoate, vinyl propionate, vinyl decanoate, vinyl actanoate, and other monofunctional unsaturated vinyl esters of linear or branched carboxylic acids comprising 1 to 14 carbon atoms, which as homopolymers have glass transition temperatures below about xe2x88x9210xc2x0 C. Preferred vinyl ester monomers include vinyl laurate, vinyl caprate, vinyl 2-ethylhexanoate, and mixtures thereof.
Additional other vinyl monomers which, as homopolymers, have glass transition temperatures higher than about xe2x88x9210xc2x0 C. to 0xc2x0 C., such as vinyl acetate, acrylonitrile, mixtures thereof and the like, may optionally be utilized in conjunction with one or more of the acrylate, methacrylate and vinyl ester monomers provided the glass transition temperature of the resultant polymer is below about xe2x88x9210xc2x0 C.
Suitable comonomers include nonpolar, ionic, polar monomers and mixtures thereof. In addition to using one or more acrylate monomers as a comonomer, as described above, the following are non-limiting examples of comonomers:
(A) ionic comonomers, such as sodium methacrylate, ammonium acrylate, sodium acrylate, (I) trimethylamine p-vinyl benzimide, (II) 4,4,9-trimethyl-4-azonia-7-oxo-8-oxa-dec-9-ene-1-sulphonate, (III) N,N-dimethyl-N-(xcex2-methacryloxyethyl) ammonium propionate betaine, (IV) trimethylamine methacrylimide, (V) 1,1-dimethyl-1(2,3-dihydroxypropyl)amine methacrylimide; any zwitterionic monomer and the like;
(B) non-polar comonomers include but are not limited to, 4-methyl-2-pentyl acrylate, 2-methylbutyl acrylate, isoamyl acrylate, sec-butyl acrylate, n-butyl acrylate, isodecyl methacrylate, t-butyl acrylate, t-butyl methacrylate, isobornyl acrylate, octyl acrylamide, methylmethacrylate, isononyl acrylate, isodecyl acrylate, styrene and the like, and the combination thereof.
(C) Polar comonomers may or may not contain a dissociable hydrogen. Examples of suitable polar comonomers include organic carboxylic acids comprising 3 to about 12 carbon atoms and having generally 1 to about 4 carboxylic acid moieties. Nonlimiting examples of such monomers acrylic acid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid, maleic acid, xcex2-carboxyethylacrylate and the like. In addition suitable polar comonomers include acrylamide, methacrylamide, 2-hydroxyethyl acrylate, and the like.
In addition, one class of suitable comonomers are amino-functional monomers having a nucleus or portion of the nucleus of the general formula (a): 
wherein
R1 is xe2x80x94H, xe2x80x94CH3, xe2x80x94CH2CH3, cyano or carboxymethyl;
R2 is a hydrocarbyl radical comprising 1 to about 12 carbon atoms;
R3 and R4 are independently H or an alkyl group containing 1 to about 12 carbon atoms or an arylalkyl group or together form a cyclic or heterocyclic moiety;
L is carbon-carbon bond, O, NH or S; and
x is an integer of 1 to 3.
Nonlimiting examples of comonomers according to formula (1) include N,N-dimethyl-aminoethyl(methyl)acrylate, N,N-dimethylaminopropyl-(meth)acrylate, t-butylaminoethyl(methyl)acrylate and N,N-diethylaminoacrylate.
Another class of suitable comonomers are comonomers having a nucleus or portion of the nucleus of the general formula (2): 
wherein
R1 is H, xe2x80x94CH3, xe2x80x94CH2CH3, cyano or carboxymethyl;
R2 is a hydrocarbyl radical comprising 1 to about 12 carbon atoms;
R5 is xe2x80x94Oxe2x80x94, alkylene oxide comprising 1 to 5 carbon atoms, or phenoxy oxide, wherein the alkylene oxide would include, xe2x80x94CH2 Oxe2x80x94, xe2x80x94CH2CH2Oxe2x80x94, xe2x80x94CH2(CH)CH3Oxe2x80x94, and the like;
R6 is H, xe2x80x94C6H4OH, or xe2x80x94CH3 
L is a carbon-carbon bond, O, NH or S; and
x is an integer with the proviso that when R5 is xe2x80x94Oxe2x80x94, x is an integer of 1-3.
Nonlimiting examples of comonomers according to formula (2) include hydroxyethyl (meth)acrylate, glycerol mono(meth)acrylate and 4-hydroxybutyl (meth)acrylate, acrylate terminated poly(ethylene oxide); methacrylate terminated poly(ethylene oxide); methoxy poly(ethylene oxide) methacrylate; butoxy poly(ethylene oxide) methacrylate; acrylate terminated poly(ethylene glycol); methacrylate terminated poly(ethylene glycol); methoxy poly(ethylene glycol) methacrylate; butoxy poly(ethylene glycol) methacrylate and mixtures thereof.
Yet another class of suitable comonomers are amido-functional monomers having a nucleus or portion of the nucleus of the general formula (3): 
wherein
R1 is H, xe2x80x94CH3, xe2x80x94CH2CH3, cyano or carboxymethyl; and
R3 R4 are independently H or an alkyl group containing 1 to about 12 carbons or an arylalkyl group or together form a cyclic or heterocyclic moiety.
Nonlimiting examples of comonomers according to formula (3) include N-vinyl pyrrolidone, N-vinyl caprolactom acrylamide or N,N-dimethyl acrylamide.
Nonlimiting examples of other suitable comonomers that do not fall within the above classes but are within the scope of permissible comonomers include (meth)acrylonitrile, furfuryl (meth)acrylate and tetrahydrofurfuryl (meth)acrylate, 2-vinyl pyridine, and 4-vinyl pyridine.
Typically, when a comonomer is present, the relative amounts by weight of the alkyl (meth)acrylate monomer(s) and the comonomer is in the range of about 99.5/0.5 to 75/25, and preferably is in the range of 98/2 to 92/8.
A modifier may be used to regulate the solvent soluble portion of the microspheres and it is added to the polymerization mixture in an amount sufficient to provide a solvent soluble portion that is in the range of 30-98%, preferably in the range of 40-95%. Various modifiers may be used within the scope of this invention and the amounts used are those that sufficiently provide the microspheres with a solvent soluble portion. Such amounts would range, for example for solvents from 5-30%, for tackifiers and/or plasticizers from 1-30% and for chain transfer agents, up to about 0.15%.
Particularly useful modifiers are chain transfer agents. To control the molecular weight of the polymer being formed in the microsphere it is desirable to use a chain transfer agent or modifier. Many halogen-and sulfur-containing organic compounds function well as chain transfer agents in free radical polymerizations. Non-limiting examples of such agents are: carbon tetrabromide, carbon tetrachloride, dodecanethiol, iso-octylthioglycolate, butyl mercaptan, and tertiary-dodecyl mercaptan. In this invention it is efficacious to employ long chain mercaptans such as dodecanethiol. The amount of chain transfer agent suitable for these microsphere polymerizations is calculated on a weight basis to the entire polymerizable content. The chain transfer agent is preferably added at up to about 0.15% more preferably up to about 0.12% and most preferably up to about 0.08%. These levels are adequate to provide a soluble polymer content in the microsphere of up to about 98%.
The microsphere adhesive composition may also contain a crosslinking agent. Examples of useful crosslinking agents include, but are not limited to: multifunctional (meth)acrylate(s), e.g., butanediol diacrylate or hexanediol diacrylate or other multifunctional crosslinkers such as divinylbenzene and mixtures thereof. When used, crosslinker(s) is (are) added at a level of up to about 0.15 equivalent weight percent, preferably up to about 0.1 equivalent weight percent, of the total polymerizable composition with the proviso that the combination of crosslinking agent and modifier concentrations are chosen to obtain a microsphere with 30 to 98% solvent soluble portion.
The microspheres of the present invention are prepared by suspension polymerization using either a one-step or two-step process as described in detail below. Suspension polymerization is a procedure wherein a monomer is dispersed in a medium (usually aqueous) in which it is insoluble. The polymerization is allowed to proceed within the individual polymer droplets. Monomer soluble free-radical initiators are preferably used. The kinetics and the mechanism are those for the corresponding bulk polymerization under similar conditions of temperature and initiator concentration.
Initiators affecting polymerization are those that are normally suitable for free-radical polymerization of acrylate monomers. Examples of such initiators include thermally-activated initiators such as azo compounds, hydroperoxides, peroxides and the like and photoinitiators such as benzophenone, benzoin ethyl ether and 2,2-dimethoxy-2-phenyl acetophenone. Other suitable initiators include lauroyl peroxide and bis(t-butyl cyclohexyl)peroxy dicarbonate. The initiator is present in a catalytically effective amount sufficient to bring about high monomer conversion in a predetermined time span and temperature range. Typically, the initiator is present in amounts ranging from 0.1 to approximately 2 parts per weight per 100 parts by weight of the polymerizable monomer starting materials.
Parameters that affect the concentration of initiator employed include the type of initiator and particular monomer and/or monomers involved. It is believed that catalytically effective concentrations range from about 0.1 to about 2 percent by weight of the total monomers and more preferably, from about 0.20 to about 0.70 percent by weight monomers and/or monomers.
Optionally, a polymeric stabilizer may be used. Advantageously, the presence of the stabilizer permits the use of relatively low amounts of surfactant while still obtained microspheres.
Any polymeric stabilizer that effectively provides sufficient stabilization of the final polymerized droplets and prevents agglomeration within a suspension polymerization process is useful in the present invention. When used, a polymeric stabilizer will typically be present in the reaction mixture in an amount by weight of about 0.1 to about 3 parts by weight per 100 parts of polymerizable monomer, and more preferably will be present in an amount by weight of about 0.1 to about 1.5 parts by weight per 100 parts of polymerizable monomer.
Exemplary polymeric stabilizers include salts of polyacrylic acids of greater than 5000 molecular weight average (for example, ammonium, sodium, lithium and potassium salts), carboxy modified polyacrylamides (for example, Cyanamer(trademark) A-370 from American Cyanamid), copolymers of acrylic acid and dimethylaminoethylmethacrylate and the like, polymeric quaternary amines (for example, General Analine and Film""s Gafquat(trademark) 755, a quaternized polyvinylpyrollidone copolymer, or Union Carbide""s xe2x80x9cJR-400xe2x80x9d, a quaternized amine substituted cellulosic), cellulosics, and carboxy-modified cellulosics (for example, Hercules"" Natrosol(trademark) CMC Type 7L, sodium carboxy methycellulose).
Surfactants will typically be present in the reaction mixture in an amount of no greater than about 5 parts by weight per 100 parts by weight of polymerizable monomer, preferably no greater than about 3 parts by weight, and most preferably in the range of 0.5 to 1.5 parts by weight per 100 parts by weight of polymerizable monomer.
Useful surfactants include anionic, cationic, nonionic or amphoteric surfactants and include but are not limited to anionic surfactants, such as alkyl aryl sulfonates, for example sodium dodecylbenzene sulfonate and sodium decylbenzene, sodium and ammonium salts of alkyl sulfates, for examples sodium lauryl sulfate, and ammonium lauryl sulfate; nonionic surfactants, such as ethoxylated oleoyl alcohol and polyoxyethylene octylphenyl ether; and cationic surfactants, such as a mixture of alkyl dimethylbenzyl ammonium chlorides wherein the alkyl chain contains from 10 to 18 carbon atoms. Amphoteric surfactants are also useful in the present invention and include for example sulfobetaines, N-alkylaminopropionic acids, and N-alkybetaines.
To initiate the polymerization reaction, a sufficient number of free radicals must be present. This may be achieved through several means that are well known in the art, such as heat or radiation free-radical initiation. For example, heat or radiation can be applied to initiate the polymerization of the monomers, which is an exothermic reaction. However, it is preferred to apply heat until thermal decomposition of the initiators generates a sufficient number of free radicals to begin the reaction. The temperature at which this occurs varies greatly depending upon the initiator used.
In addition, deoxygenation of the polymerization reaction mixture is often desirable. It is well known that oxygen dissolved in the reaction mixture can inhibit polymerization and it is desirable to expel this dissolved oxygen. Although, an inert gas bubbled into the reaction vessel or through the reaction mixture is in effective means of deoxygenation, other techniques for deoxgenation that are compatible with suspension polymerization can be used. Typically, nitrogen is used to deoxygenate, although any of the Group VIIIA (CAS version) inert gases are also suitable.
While specific time and stirring speed parameters are dependent upon monomers, and initiators, it is desirable to predisperse the reaction mixture until the reaction mixture reaches a state where the average monomer droplet size is between about 1 xcexcm and 300 xcexcm and preferably between 20 xcexcm and 70 xcexcm. The average particle size tends to decrease with increased and prolonged agitation of the reaction mixture.
Preferably, stirring and nitrogen purge are maintained throughout the reaction period. Initiation is begun by heating the reaction mixture. Following polymerization, the reaction mixture is cooled.
In a one-step process both the alkyl (meth)acrylate monomer and any optional comonomer are present together in the suspension at the initiation of polymerization. In a two-step process any optional comonomer is typically added after the initial exotherm resulting from polymerization of the alkyl (meth)acrylate monomer has peaked, but could be added at any point after polymerization has started. The other components, such as the initiator, stabilizers (if used), surfactants and modifiers are present in the reaction mixture as described in the processing steps herein above.
Following polymerization, a stable aqueous suspension of microspheres at room temperature is obtained. The suspension may have non-volatile solids contents of from about 10 to about 70 percent by weight. Upon prolonged standing, the suspension typically separates into two phases, one phase being an aqueous, essentially polymer microsphere-free phase and the other phase being an aqueous suspension of the polymeric microspheres, that is, the microsphere-rich phase. The aqueous suspension of microspheres may be utilized immediately following polymerization, because the suspension of microspheres of the present invention is particularly stable to agglomeration or coagulation. Advantageously, the microspheres of the present invention can be easily coated from an aqueous solution. Surprisingly, the microspheres of the present invention are well suited for conventional coating techniques and have enhanced fluid processing characteristics.
The microsphere-rich phase can be diluted with an additional amount of water or solvent, or redispersed upon shaking or other means of agitation. Generally, this aqueous suspension can be coated onto a backing or other substrate being employed using conventional coating methods, such as slot die coating, to provide an adhesive coating. The microspheres can be compounded with various rheology modifiers and/or latex adhesives or xe2x80x9cbindersxe2x80x9d. Typically, the adhesive coating which, when dried, exhibits a dry coating weight in the range of 0.2 to about 2 grams per square foot to provide an adhesive-coated sheet material in which the adhesive coating comprises polymeric microspheres, polymeric stabilizer, surfactant, and optionally rheology modifiers, and/or latex adhesives. Alternatively, the microspheres may be isolated and combined with an organic solvent if desired prior to coating them onto the backing.
Properties of the pressure-sensitive adhesives of the present invention can be altered by the addition of a tackifying resin(s) and/or plasticizer(s) after the polymerization. Preferred tackifiers and/or plasticizers for use herein include hydrogenated rosin esters commercially available from such companies as Hercules, Inc. under the trade names of Foral(trademark), Regalrez(copyright) and Pentalyn(trademark). Tackifying resins also include those based on t-butyl styrene. Useful plasticizers include but are not limited to dioctyl phthalate, 2-ethylhexyl phosphate, tricresyl phosphate and the like. If such tackifiers and/or plasticizers are used, the amounts used in the adhesive mixture are amounts effective for the known uses of such additives.
Optionally, adjuvants, such as, rheology modifiers, colorants, fillers, stabilizers, pressure-sensitive latex binders and various other polymeric additives can be utilized. If such adjuvants are used, the amounts used in the adhesive mixture are amounts effective for the known uses of such adjuvants.
Suitable backing or substrate materials for use in the present invention include, but are not limited to, paper, plastic films, cellulose acetate, ethyl cellulose, woven or nonwoven fabric comprised of synthetic or natural materials, metal, metallized polymeric film, ceramic sheet material and the like. Generally the backing or substrate material is about 50 xcexcm to about 155 xcexcm in thickness, although thicker and thinner backing or substrate materials are not precluded.
Particularly useful articles prepared using the microsphere adhesives of the present invention include repositionable adhesive products such as repositionable note and paper products, repositionable tape and tape flags, easel sheets, repositionable glue stick and the like, but may also include other non-repositionable industrial commercial, and medical adhesive products.
The present invention is further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention. All materials are commercially available or known to those skilled in the art unless otherwise stated or apparent. The following examples are illustrative in nature and are not intended to limit the invention in any way.